PHOTOLUMINESCENCE AND RAMAN SCATTERING OF PURE GERMANIUM/SILICON SHORT PERIOD SUPERLATTICE

Pure Ge/Si short period superlattice (SPS) samples grown by gas source molecular beam epitaxy (GS-MBE) were studied by photoluminescence and Raman scattering. For SPS samples with Germanium layer thickness (L_Ge) of 1.5 monolayer (ML), a new band of photoluminescence is observed for silicon layer thickness (L_Si) in an intermediate range of 1.9-2.9 nm. In contrast to pure Ge/Si quantum wells, the energy of the new band shows a red-shift with the increase of L_Si. Raman scattering results show that when the intensity of the photoluminescence of the new band reaches a maximum, the Raman shift relating the vibration of Si-Si reaches a minimum. It is therefore considered that the new band of the pure Ge/Si SPS is related with some kind of strain relaxation process.